Find the right air-conditioner size for your room - in BTU/hr and tonnes. Adjusts for room area, ceiling height, sun exposure, occupants and kitchen heat. Get an oversized AC and you waste energy; undersized and the room never cools.
1 sq m ≈ 10.76 sq ft
Recommended AC
1.0 ton
3,750 BTU/hr
BTU per hour
3,750
Tonnage
0 ton
1 ton = 12,000 BTU
Rule-of-thumb sizing. Indian summers may need slightly larger units in cities like Delhi or Chennai. Inverter ACs auto-modulate, so being within 10% is fine.
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Choosing the right AC size is one of the most impactful decisions in setting up your home's cooling - get it wrong and you'll either struggle with inadequate cooling on peak summer days or waste 20-30% on electricity bills for years. Indian summers, especially in cities like Delhi, Ahmedabad, Hyderabad and Chennai where temperatures cross 40°C for weeks, demand correctly-sized cooling. An undersized AC runs continuously, never quite reaching set temperature, and humidity stays high; an oversized AC cools quickly then short-cycles, failing to remove humidity and creating a clammy, uncomfortable feel.
The standard rule of thumb - 1 ton per 100-120 sq ft - works as a starting point but ignores critical Indian conditions: harsh west-facing sun, high outdoor temperatures (40°C+ in summer vs the 32°C the formula was designed for), poor wall insulation in older buildings, large families, and tropical humidity. This calculator adjusts for all of these factors. The output is in both BTU/hr (the technical unit used in cooling specifications) and tons (1 ton = 12,000 BTU/hr, the more familiar Indian retail unit). Common AC sizes in India: 0.8 ton, 1.0 ton, 1.5 ton (the most popular for bedrooms), 2 ton (large bedrooms / small living rooms), 2.5 ton, and 3 ton for halls.
Enter room area in square feet (or square metres).
Adjust ceiling height if not 8 ft.
Toggle 'sunny side' if the room gets direct afternoon sun.
Enter typical occupants and whether it's a kitchen.
Read recommended BTU and AC tonnage.
Base load = 25 BTU per sq ft. Ceiling height >8 ft scales linearly. Sunny rooms add 10%. Each occupant beyond 2 adds 600 BTU. Kitchens add 4,000 BTU for cooking heat.
BTU = (Area × 25) × Ceiling factor × (1 + Sun%) Tons = BTU / 12,000
Base cooling load: 25 BTU per square foot of floor area for typical residential rooms with 8-foot ceilings, average sun exposure, and 2-person occupancy. This is the starting baseline. For Indian conditions where summer indoor heat load is higher than international references, the calculator uses slightly more conservative figures than ASHRAE's US-based recommendations.
Adjustments applied: Ceiling height - for ceilings above 8 ft (most Indian apartments have 9-10 ft), scale linearly: BTU × (height/8). High-ceilinged 10 ft rooms need 25% more cooling. Sun exposure - west or south-facing rooms with large windows get direct afternoon sun and add 10-15%. Occupants - each additional person beyond 2 adds 600 BTU (body heat dissipation). Kitchens - cooking adds 4,000 BTU for the heat from stoves, ovens and the refrigerator's heat rejection.
Tonnage conversion: divide BTU by 12,000 to get tons. A 12,000 BTU/hr AC = 1 ton; 18,000 BTU = 1.5 ton; 24,000 BTU = 2 ton. Always round up to the nearest standard size - undersizing is worse than slight oversizing. Choose inverter ACs over fixed-speed for any size above 1 ton - inverter compressors modulate capacity to actual heat load, saving 15-25% on electricity vs fixed-speed of the same nominal rating. Pair the right size with a 5-star BEE rating for maximum efficiency.
Base: 130 × 25 = 3,250 BTU. Sun: +10% = 3,575 BTU. 2 occupants: no extra. Result: 3,575 BTU. Convert to tons: 0.3. Round up to 1.0 ton (smallest standard size). Choose 1.0 ton 5-star inverter split AC.
Base: 180 × 25 = 4,500. Ceiling: × 10/8 = 5,625. Sun: +10% = 6,188 BTU. Result: 6,188 BTU = 0.52 ton. Round up to 1.0 ton. For Delhi/Chennai conditions, upgrade to 1.5 ton for comfort margin.
Base: 280 × 25 = 7,000. Ceiling × 11/8 = 9,625. Sun +10% = 10,588. Plus 3 extra occupants × 600 = 12,388 BTU = 1.03 ton. Round up to 1.5 ton. Consider 2.0 ton for typical 4-6 person family use.
Up to ~120 sq ft (12 m²) at 8 ft ceiling height. 1.5 ton suits up to ~180 sq ft, 2 ton up to 250 sq ft.
Same tonnage maths. But split ACs have higher SEER ratings on average - check the BEE star rating for energy efficiency.
Inverter ACs auto-adjust capacity, so they're more forgiving of slight oversizing. Still aim for the right size for best efficiency.
Direct afternoon sun adds significant heat through windows. West-facing rooms can need 10-20% more cooling.
Renovating, decorating or estimating utilities at home almost always reduces to three numbers - area, volume, and cost. Get any of them wrong by 10% and you're either short of paint and tile, or you've over-ordered and have to return material. This calculator uses the same wastage allowances, packing rules and unit conversions that contractors and material suppliers actually use in India.
Use it together with the paint, tile, electricity bill and BTU calculators to plan a complete renovation budget. Indian states have very different electricity tariffs and material prices, so the calculators expose state-wise tariffs (Maharashtra MSEDCL, Tamil Nadu TANGEDCO, Delhi BSES, Karnataka BESCOM, etc.) and let you override defaults to match your supplier's pricing.
The BTU Calculator is part of the Home & Lifestyle suite on Online Calculator Tools, alongside 6 related calculators. All tools share the same UI patterns, the same privacy-first rendering (nothing is sent to a server), and the same commitment to showing the formula and assumptions behind every result.
